In the market of solid-state image-capturing devices, there has recently been a rapid increase in the sales of those of the CMOS sensor-type for use in mobile telephones. Each pixel section of a CMOS sensor-type solid-state image-capturing device includes a photoelectric conversion unit (hereinafter referred to as a pixel) for generating a signal charge according to the incident light, and an amplification unit for converting the signal charge of the photoelectric conversion unit into a signal voltage and amplifying the signal voltage.
Solid-state image-capturing devices not only simply capture video images, but may also detect a motion of an object on a captured image screen of the solid-state image-capturing device. For example, they are used in motion detection systems for continuously capturing an image of the same field of view and detecting a person entering this field of view so as to control various devices in response to the entrance of the person or to inform or record the entrance of the person.
As a method for detecting such a motion of a video image on an captured image screen, there is Method 1 in which a motion is detected based on comparison between signal outputs of the same pixel from two consecutive frames (Patent Document No. 1). There is also Method 2 in which the integration time is varied while treating adjacent pixels as a pair so as to adjust the gain and detect a motion based on the differential signal (Patent Document No. 2).
The former Method 1 requires a frame memory, thereby resulting in a large circuit scale and increasing the power consumption. Moreover, a cost increase cannot be avoided. With the latter Method 2, a differential signal is generated at an edge portion of an object, thereby generating an erroneous detection signal, and resulting in a poor motion detection accuracy.
Particularly, when capturing a color video image, where one employs the Bayer arrangement, a typical color filter arrangement (2×2-pixel sets, in which G (green) color filters are arranged diagonally, with an R (red) and a B (blue) color finger arranged in the remaining positions), pixel signals of the same G color, which occur at least at every other pixels, will be used, thereby increasing the erroneous detection signal, thus further deteriorating the motion detection accuracy.
Moreover, the motion detection operation detects whether there is an object that is moving constantly. Therefore, there is a demand for a solid-state image-capturing device or a motion detection system having a small power consumption.